TRV Question

Mike T., Swampeast MO

Given the ability of a single TRV to handle the entire load and a single radiator able to handle the load in moderate weather:

Can two radiators with TRVs in the SAME space be connected in series--i.e. one TRV controlling multiple radiators?

BOTH currently have TRVs and only in the coldest weather does the second get warm.

The ONE running has the LOWEST delta-t in the entire system.

Plain cast iron boiler already operating at very low temperature.

Would doing this just increase the system delta-t and lower return temps even farther?

Mike Kraft

I've done it............

and no problems.As far as a lower drop my mind see's it being very slight being that the emitters are already in the same room and it sounds like but one of them support the load already.Sharing the two emitters from one TRV will still offer the same amount of BTU's but the TRV may close sooner than later now.

cheese

Dan Peel

sure can

In series or parallelled beyond the TRV for improved balance in the room from the same BTU inputs. Dan

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Steve Ebels

I've stacked

As many as 3 rads on one TRV. With the rads in series you want to be aware of the decreased output of the donwnstream units. They're seeing lower entering water temp. You can generate a whale of a delta T in a loop like that. 60-70* isn't uncommon from what I've experienced.

Mike T., Swampeast MO

Thanks all

Didn't think there would be any problem save that "whopper" of a delta-t across the rads. Will be interesting to feel the effect.

hydronicsmike

Have to be careful though....

...I have seen boilers exposed to thermal shock and condensation if the deltaT gets too large.

One specific job I remember, the guy had 4 (larger) radiators in a larger space tied in series (with one TRV) and had a deltaT between the first radiators supply and last radiators return of close to 80°F. Boiler had to be replaced and mixing with boiler protection was added to eliminate the boiler issue in the future.

Basically, in his case, one TRV did the job, no problem. But what else is going on in the system, one should keep in mind as well. Protect your boilers! After that, pretty much anything goes.

I also think that multiple radiators in series add mass. If you had 4 radiators and the TRV is satisfied, the water in the radiators may potentially cool down to room temp, if the TRV is off long enough. Imagine another part of the system requiring heat (which could be even smaller) with the boiler at 160°F, can you see what could happen if you introduced a rather large amount of cold (70°F) water out of the turned off radiator(s)back to the hot boiler as soon as the TRV opens up again?

No doubt that in most cases we might not see this issue occur, but it does happen. Are there any boiler manufacturers that could back this up? Any replaced sections lately?

Just a thought.

Mike